In recent years, in accordance with development of wireless techniques, usage of performing high-speed communication in a relatively small communication area such as radio LAN (Local Area Network) in addition to transmitting a small volume of content such as speech and email in a large communication area typified by mobile telephones, is spread.
Further, usage of using only a very limited location (that is, specific location) such as DSRC (Dedicated Short Range Communication) as a communication area, and that allows only users located in the specific location to communicate, is spread.
In the future, usage of downloading a large volume of content to a terminal a user carries or a terminal provided in a car, in a short period of time, is expected to be spread. However, such a large volume of content may include a large amount of personal information, and, if the content is image content such as movies, the content may be charged content.
Taking into consideration such a situation in the future, an increased demand for establishment of a communication system that enables high-speed large-volume communication positively with only communicating parties located in a specific location is expected.
FIG. 1 to FIG. 3 show conceptual diagrams illustrating a method for realizing a communication area of an ETC (Electronic Toll Correction System) as a conventional example of a communication system where communication is possible only with communicating parties located in a specific location. FIG. 1 to FIG. 3 show a case where vehicle 12-1 having first terminal 11-1 and vehicle 12-2 having second terminal 11-2 reach the vicinity of antenna 14 connected to radio section 13 of the communicating party.
As shown in FIG. 1, when service area AR1 of radio section 13 is made relatively large using antenna 14 with weak directivity, both first terminal 11-1 and second terminal 11-2 start communication with radio section 13, and cases occur where interference occurs, both terminals cannot communicate, or different terminals receive information data.
On the other hand, as shown in FIG. 2, when service area AR2 of radio section 13 is made relatively small, substantial communication time cannot be ensured when the moving speed of a vehicle is fast, and it is necessary to reduce the speed of the vehicle or bring the vehicle to a stop to ensure communication time.
To solve these problems, as shown in FIG. 3, Patent Document 1 discloses a technique of forming service area AR3 using first directivity and service area AR4 using second directivity by using a beam switching antenna as antenna 14. By this means, even if the moving speed of the vehicle is fast, terminals 11-1 and 11-2 can communicate without interference both in service areas AR3 and AR4.
Patent Document 1: Japanese Patent Application Laid-Open No. HEI11-185083